Best way to make a concept for a videogame model?
I will do my best to answer your question within the bounds of the Blender Stack Exchange focus.

If you've ever seen professional concept art, they often have 3 view of a character/concept object.

-Frontal
-Profile
-close up

This is so the entire concept can be displayed. In blender, the frontal and profile views are often used in character modeling.

A common practice is to enable the "insert images as planes" add-on and place the planes in front of and next to the character you are modeling.

There are many tutorials and examples of this. A quick internet search will probably prove fruitful.

I hope it helps!